Traditionally phosphate builders have been used in detergent formulations. Environmental considerations make desirable the replacement of phosphate by more environmentally friendly builders. Apart from cleaning repercussions, the replacement of phosphate can impair the stability of the detergent. Phosphate is a good moisture sink contributing to moisture management and stability of the detergent. The majority of the builders which can be used as replacement for phosphate are incapable of acting as moisture sinks—furthermore they are usually hygroscopic, contributing to the instability and degradation of the detergent. This has a greater impact in detergents which comprise moisture sensitive ingredients such as bleach and enzymes.
A consequent problem found with many phosphate replacements, such as aminocarboxylic builders, is their instability and difficulty in handling under the high ambient temperature and humidity conditions that can be found in manufacturing plants or during transport and storage. This problem can be particularly acute during summer months or during a rainy season. Particulate materials can lose their flowability and—in cases in which the materials are highly hygroscopic—they can become sticky, crusty or turn into liquids, making them unsuitable for use in detergent formulations.
Aminocarboxylic compounds such as methylglycine diacetic acid and salts thereof are suitable compounds as phosphate replacement in detergent compositions. The use thereof is, however, in most cases restricted to their use in liquid applications. This is due to the fact that these materials in solid form tend to be highly hygroscopic. Hence in typical manufacturing conditions, storage and/or transport, they can lose their stability and even return to its liquid form. It is possible to avoid many of these issues by the use of protective engineering measures such as dehumidification of the ambient air. However these can be very expensive to implement—especially in large manufacturing plants.
There have been several attempts to convert methylglycine diacetic acid and salts thereof into solid particles. Some of the processes involved are quite cumbersome and sometimes the resulting particles are not totally satisfactory from a handling, transport, storage and in-product stability viewpoint. Other drawbacks found with some of the particles disclosed in the literature is that the particles include additional materials that can be inert in terms of cleaning, thereby contributing to the cost of the product without providing any benefits and in some cases even having negative impact on cleaning, such as leaving residues on the cleaned items.
Turning to the existing art, US 2008/0045430 discloses a mixed powder or mixed granule containing at least 80% by weight of a mixture of (a) from 5 to 95% by weight of at least one glycine-N,N-diacetic acid derivative of general formula MOOC—CHR—N(CH2COOM)2 where R is C1-12 alkyl and M is alkali metal, (b) from 5 to 95% by weight of at least one polyethylene glycol or of at least one nonionic surfactant or of a mixture thereof or of a polymer selected from the group consisting of polyvinyl alcohols, polyvinylpyrrolidones (PVP), polyalkylene glycols and derivatives thereof. The powder or granule of '430 comprises materials that may not contribute to cleaning and can leave residues on the cleaned items. Moreover, the dissolution of the powder or granule seems to rely on the melting or dissolution of component b). The current tendency on automatic cleaning processes, such as laundry and dishwashing, is to use lower temperatures. There is a risk that the powder or granule would not dissolve sufficiently rapidly at low temperature. Although, the powder or granule has improved handleability there is still room to improve their physical properties especially in conditions of high ambient humidity.
WO2009/092699 discloses a process for the preparation of free flowing MGDA granules having low hygroscopicity. This comprises heating a concentrated slurry comprising MGDA and spray granulating said slurry. The process requires the preparation of the concentrated slurry before processing further and this could be difficult depending on the solid concentration used. The process is also limited by the requirement that the drying air used in the spray-granulation has to be less than 120° C. This means that drying rates will be limited compared to processes using higher drying air temperatures.
The objective of the present invention is to provide a particle which maintains its physical structure and it is stable during storage, transport, manufacture and at the same time is stable and robust in detergent compositions. The particle should be resilient to moisture.